Measurement of the Vibrational Relaxation Time of CO behind a Shock Wave by Infrared Emission

1957 ◽  
Vol 27 (1) ◽  
pp. 315-316 ◽  
Author(s):  
M. W. Windsor ◽  
Norman Davidson ◽  
Ray Taylor
Keyword(s):  
Shock Wave ◽  
Relaxation Time ◽  
Vibrational Relaxation ◽  
Infrared Emission

The Master Equation for the Dissociation of a Dilute Diatomic Gas IX. Rotation–Vibration Relaxation Times

1973 ◽  
Vol 51 (12) ◽  
pp. 1923-1932 ◽  
Author(s):  
E. Kamaratos ◽  
H. O. Pritchard
Keyword(s):  
Shock Wave ◽  
Relaxation Time ◽  
Vibrational Relaxation ◽  
Transition Probabilities ◽  
Transition Probability ◽  
Relaxation Times ◽  
Rotational Relaxation ◽  
Relaxation Matrix ◽  
Coupling Case ◽  
Increasing Temperature

The relationships between individual rotational or vibrational transition probabilities and the eigenvalues of the 172nd order relaxation matrix describing the rotation–vibration–dissociation coupling of ortho-hydrogen are explored numerically. The simple proportionality between certain transition probabilities and certain eigenvalues, which was found previously in the vibration–dissociation coupling case, breaks down. However, it is shown that at 2000°K the second smallest eigenvalue of the relaxation matrix (dn−2), hitherto regarded as determining the "vibrational" relaxation time, is related more to the transition probability assigned to the largest rotational gap which lies in the first (ν = 0 ↔ ν = 1) vibrational gap, i.e. to the transition ν = 0, J = 5 ↔ ν = 0, J = 7, than to anything else; this clearly supports an earlier suggestion that the transient which immediately precedes dissociation in a shock wave has to be regarded as a rotation–vibration relaxation time rather than a vibrational relaxation time. It is suggested that the Lambert–Salter relationships can be rationalized on this assumption.An analysis is then made of the energy uptake associated with each eigenvalue at three temperatures. At 500°K, the greatest energy increment is associated with two eigenvalues (dn−13 and dn−24) and can be characterized as essentially a rotational relaxation: the calculations confirm that the observed rotational relaxation time should first decrease and then increase with increasing temperature, as was recently found to be the case experimentally. At 2000°K, large energy increments are associated with several eigenvalues between dn−2 and dn−14, and at 5000°K, with most of the eigenvalues dn−2 to dn−23; thus, the higher the temperature, the more complex is the (T–VR) rotation–vibration relaxation. Further, relaxation times for the same temperature measured by ultrasonic and shock-wave techniques need not agree.

On the interpretation of measured rotational and vibrational relaxation times. II. Sudden change experiments

1976 ◽  
Vol 54 (15) ◽  
pp. 2372-2379 ◽  
Author(s):  
Huw Owen Pritchard
Keyword(s):  
Shock Wave ◽  
Relaxation Time ◽  
Vibrational Relaxation ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Sudden Change ◽  
Heat Bath ◽  
Mode Analysis ◽  
Wave Excitation ◽  
Measured Relaxation

This paper examines, in terms of the normal-mode analysis developed earlier (Part I), the nature of relaxations in which a diatomic gas, highly diluted in a heat bath of inert gas atoms, is subjected to a sudden change as in shock-wave excitation or laser schlieren experiments.It is shown in detail how the observed relaxation time in a shock-wave excitation to a fixed final temperature depends on the initial temperature. At the same time, it is confirmed that the characterisation as 'mainly rotational' of the measured relaxation time in H2 when it is heated from room temperature to 1500 K in a shock wave is perfectly plausible.On the other hand, the calculations show that in laser schlieren experiments in which the v = 1, J = 1 level of H2 is overpopulated, the vibrational relaxation time of H2 at the temperature in question is recovered, although interesting effects should appear if other J levels were populated initially, or if the experiments were carried out at much higher ambient temperatures.The calculations also demonstrate that it is not generally possible to derive relaxation times by following the variation in population of any particular level of the molecule: multiple overshoots sometimes occur, and apparent relaxation times both longer or shorter than the true relaxation times could often result from attempts to follow level populations as a function of time.

On the breakdown of characteristics solutions in flows with vibrational relaxation

1967 ◽  
Vol 27 (1) ◽  
pp. 49-57 ◽  
Author(s):  
B. S. H. Rarity
Keyword(s):  
Relaxation Time ◽  
Mach Number ◽  
Supersonic Flow ◽  
Steady Flow ◽  
Speed Of Sound ◽  
Vibrational Relaxation ◽  
Precise Measure ◽  
Derivatives Of ◽  
Relaxing Gas ◽  
Flow Case

The breakdown of the characteristics solution in the neighbourhood of the leading frozen characteristic is investigated for the flow induced by a piston advancing with finite acceleration into a relaxing gas and for the steady supersonic flow of a relaxing gas into a smooth compressive corner. It is found that the point of breakdown moves outwards along the leading characteristic as the relaxation time decreases and that there is no breakdown of the solution on the leading characteristic if the gas has a sufficiently small, but non-zero, relaxation time. A precise measure of this relaxation time is derived. The paper deals only with points of breakdown determined by initial derivatives of the piston path or wall shape. In the steady-flow case, the Mach number based on the frozen speed of sound must be greater than unity.

scholarly journals The survival of PAHs and (hydro)carbon nanoparticles in H II regions

2015 ◽  
Vol 11 (A29A) ◽  
Author(s):  
Elisabetta R. Micelotta ◽  
Marco Bocchio ◽  
Aurélie Rémy-Ruyer ◽  
Melanie Köhler ◽  
Nathalie Ysard ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbon ◽  
Vibrational Relaxation ◽  
Carbon Nanoparticles ◽  
Infrared Emission ◽  
H Ii Regions ◽  
Destruction Mechanism ◽  
Hydro Carbon ◽  
First Results ◽  
Polycyclic Aromatic ◽  
Physical Response

AbstractObservations show that emission from the Unidentified Infrared (UIR) bands is strongly suppressed in H II regions. UIR bands are generally attributed to vibrational relaxation of FUV - excited Polycyclic Aromatic Hydrocarbon (PAH) molecules or hydrocarbon nanoparticles containing aromatic domains. If the strongly reduced UIR emission in H II regions is due to the suppression of the carriers, an efficient destruction mechanism is required to explain observations. The aim of this work is to clarify whether UV processing of PAHs and nanoparticles is indeed responsible for the observed lack of infrared emission. We present here our first results on the physical response to photo-processing of the proposed UIR-bands carriers.

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